How have scientists determined that most of the CO2 increases ...

[chads108]

How have scientists determined that most of the CO2 increases have come from human burning of fossil fuels, rather than natural sources?
 
  A) Carbon isotope analysis indicates the source is fossil carbon.
  B) There haven't been enough volcanic eruptions since the observed CO2 increases to account for the additional atmospheric carbon.
  C) Prior to the industrial revolution, CO2 concentrations were negligible, while other greenhouses gases dominated the atmosphere.
  D) Paleoclimatological reconstructions which show higher CO2 concentrations than pre-industrial times.
  E) CO2 concentrations are much higher in urban areas than in rural areas, indicating fossil fuels must be the source.

Question 2

The most abundant natural greenhouse gas in the Earth's atmosphere is
 
  A) methane (CH4).
  B) carbon dioxide (CO2).
  C) ozone (O3).
  D) water vapor (H2O).
  E) nitrous oxide (N2O).

[Cnarkel]

Answer to Question 1

A

Answer to Question 2

D

[chads108]

TYSM

[samiel-sayed]

Gracias!